This invention relates to a device for detecting a jam in the neighborhood of an intermediate tray which is provided in a copying machine for temporarily supporting the copy paper after copying has been finsihed on one side thereof and until it is transported back again to the paper supplying section of the copying machine when it is operated in the two-side copying, composite copying or other multiple copying mode.
The operation of a copying machine capable of automatic two-side copying or composite copying is explained first by way of FIG. 3. Copy paper is supplied from one of paper cassettes 1 and passed through paper feeder rollers 2 and between a photosensitive drum 3 and a main charger 4 to have a toner image transferred thereonto. Thereafter, the image is fixed as the paper moves through a fixing section 5. The copy paper discharged from the fixing section 5 passes through a first switch gate 6 and moves toward a second switch gate 7 therebelow.
When the aforementioned second switch gate 7 is set for the two-side copying mode of operation, the copy paper is moved to a direction reversing section 8. The direction reversing section 8 serves to reverse the direction of motion of the incoming copy paper by alternately activating positive-rotating rollers 9 and negative-rotating rollers 10 and also by switching the direction of a movable paper guide 11 such that the back edge of the copy paper now becomes its front edge as the paper reaches a multi-gate section 12. The back side of the paper which has not been processed by the first copying cycle is now going to be exposed for copying.
The multi-gate section 12 is comprised of a plurality of gates 12a, 12b, 12c. . . arranged in the direction of motion of the copy paper. The gate corresponding to the size of the paper is opened and the paper drops into what is herein referred to as an intermediate tray 13. The paper which has been dropped into this intermediate tray 13 keeps traveling forward by the action of rollers 14 inside the multi-gate section 12 until its back edge leaves the multi-gate section 12. Its top edge advances on the intermediate tray 13 or the sheets of copy paper already piled up thereon. After it leaves the multi-gate section 12, the copy paper is transported to a front edge aligning roller 15 and is set at a specified position with its front edge in contact with a paper refeeding gate 16 at the front end of the intermediate tray 13. Thereafter, its transverse position is adjusted by means of an aligning plate (not shown) and the paper is then ready to be fed again for the processing of its second side.
After all copy paper sheets which have had images transferred onto one side only are stacked in the intermediate tray 13, the refeeding gate 16 is opened by a signal indicating that the processing of the second sides is to start. The sheets of copy paper in the intermediate tray 13 are sequentially transported one by one from the top to the aforementioned paper feeder rollers 2 through a refeeding inlet 18 by the operation of refeeding rollers 17.
What was described above is the automatic two-side copying mode of operation. When the composite copying mode of operation is desired, the aforementioned second switch gate 7 is opened in the direction of the multi-gate section 12 such that the copy paper with image transferred only to one side thereof is passed directly to the multi-gate section 12 without going through the aforementioned direction reversing section 9. The motion of the paper thereafter is the same as described above and composite images are automatically produced on one side of the paper.
With a copying machine of the type having such an intermediate tray, a jam may take place between the multi-gate section 12 and the intermediate tray 13. For this reason, it is preferable to equip the copying machine with a mechanism for detecting such a jam. One of the typical methods previously considered was to place a movable piece in the path of the paper such that the passing of a sheet of paper can be detected by the laid-down position of this movable piece. Another method was to provide an optical sensor from the top surface to the bottom surface of the paper on the intermediate tray 13 such that presence or absence of paper can be detected optically. Presence or absence of a jam can be detected by checking whether this sensor is in the ON condition or not after a specified time interval. With such previously considered mechanisms for detecting a jam, however, a jam of the type caused by a copy paper sheet which curls up and becomes wrinkled into an accordion-like shape cannot be detected because such a wrinkled sheet can still knock down the movable piece in its path to a laid-down position. An optical sensor is not effective in such a situation, especially when there are many sheets stacked in the intermedite tray 13.